CMP Groove Depth and Conditioning Disk Monitoring

ABSTRACT

Some embodiments relate to a chemical mechanical polishing (CMP) system. The CMP system includes a polishing pad having a polishing surface, and a wafer carrier to retain a wafer proximate to the polishing surface during polishing. A motor assembly rotates the polishing pad and concurrently rotates the wafer during polishing of the wafer. A conditioning disk has a conditioning surface that is in frictional engagement with the polishing surface during polishing. A torque measurement element measures a torque exerted by the motor assembly during polishing. A condition surface analyzer determines a surface condition of the conditioning surface or the polishing surface based on the measured torque. Other systems and methods are also disclosed.

BACKGROUND

Over the last four decades, the density of integrated circuits hasincreased by a relation known as Moore's law. Stated simply, Moore's lawsays that the number of transistors on integrated circuits (ICs) doublesapproximately every 18 months. Thus, as long as the semiconductorindustry can continue to uphold this simple “law,” ICs double in speedand power approximately every 18 months. In large part, this remarkableincrease in the speed and power of ICs has ushered in the dawn oftoday's information age.

Unlike laws of nature, which hold true regardless of mankind'sactivities, Moore's law only holds true only so long as innovatorsovercome the technological challenges associated with it. One of theadvances that innovators have made in recent decades is to use chemicalmechanical polishing (CMP) to planarize layers used to build up ICs,thereby helping to provide more precisely structured device features onthe ICs.

To limit imperfections in planarization, improved planarizationprocesses are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a CMP system in accordance with someembodiments.

FIG. 2 is a top view of a CMP system having a polish pad that includes aseries of concentric grooves, and a groove depth measurement elementtraversing over the polish pad.

FIG. 3 is a cross sectional side view of FIG. 2's CMP system.

FIG. 4 shows a block diagram of another CMP system in accordance withsome embodiments.

FIG. 5 is a flow diagram illustrating a method of performing aplanarization process in accordance with some embodiments.

DETAILED DESCRIPTION

The present disclosure will now be described with reference to thedrawings wherein like reference numerals are used to refer to likeelements throughout, and wherein the illustrated structures are notnecessarily drawn to scale. It will be appreciated that this detaileddescription and the corresponding figures do not limit the scope of thepresent disclosure in any way, and that the detailed description andfigures merely provide a few examples to illustrate some ways in whichthe inventive concepts can manifest themselves.

Conventional CMP techniques lack real-time feedback to adequatelyaccount for changes in the surface condition of polishing pads and/orconditioning disks. For example, an overly worn conditioning disk cancause wafers to be planarized more slowly and/or less uniformly,relative to a new conditioning disk. Thus, it is imperative to be ableto monitor the surface condition of polishing pads and/or conditioningdisks so they can be changed at an optimum time that strikes a goodbalance between maximizing the useful lifetime of the pad/disk,maximizing wafer throughput, and maximizing wafer surface uniformity.

FIG. 1 shows a block diagram of a CMP system 100 in accordance with someembodiments of the present disclosure. The CMP system 100 includesplaten 102, polishing pad 104, slurry arm 106, wafer carrier 108, andconditioning disk 110. In some embodiments, this CMP system can processwafers that are 450 mm in diameter, however it is also applicable toother wafer sizes.

Prior to wafer planarization, slurry arm 106 dispenses slurry 111, whichcontains abrasive slurry particles, onto polishing surface 112 ofpolishing pad 104 before wafer planarization occurs. Motor assembly 114,under control of CMP controller 116, then rotates the platen 102 andpolishing pad 104 (e.g., via platen spindle 118) about a polishing padaxis 120—as shown by first angular velocity arrow 122. As polishing pad104 rotates, conditioning disk 110, which can be pivoted via scan arm124 and rotated about disk axis 142, traverses over polishing pad 104such that conditioning surface 126 of conditioning disk 110 is infrictional engagement with polishing surface 112 of polishing pad 104.In this configuration, conditioning disk 110 scratches or “roughs up”polishing surface 112 continuously during polishing to help ensureconsistent and uniform planarization. Motor assembly 114 alsoconcurrently rotates a wafer housed within wafer carrier 108 about waferaxis 128 (e.g., via wafer carrier spindle 130)—as shown by secondangular velocity arrow 132. While this dual-rotation 122, 132 occurs,the wafer is “pressed” into slurry 111 and polishing surface 112 with adown-force applied by wafer carrier 108. The combination of abrasiveslurry 111, dual rotation (122, 132), and down-force planarizes thelower surface of the wafer until an endpoint for the CMP operation isreached.

To remedy shortcomings of conventional CMP systems, CMP system 100includes a surface condition analyzer 136 to determine surfacecondition(s) of polishing pad 104 and/or conditioning disk 110 inreal-time during polishing. In some cases, a feedback path 138 providesfor real-time adjustment of CMP process parameters 140 based on themeasured surface condition(s). In this way, the disclosed CMP techniquesfacilitate consistent and uniform planarization of wafers. Also, becausethe real-time measurement limits downtime for the CMP system 100 in thatwafers can be continuously processed and polishing pads 104 andconditioning disks 110 are replaced at precisely the time they arespent, these techniques can also significantly improve manufacturingthroughput while at the same time maximizing the useful lifetime ofpolishing pads 104 and conditioning disks 110.

To determine a surface condition of polishing pad 104, the polishing pad104 includes a number of grooves (e.g., 134 a, 134 b) in the polishingsurface 112. As the polishing pad 104 becomes more worn, the polishingsurface 112 is worn down, thereby reducing the depth of the grooves. Inthis way, the groove depths correspond to the condition of the polishingpad 104. To take advantage of this behavior, a depth measurement element142, such as an acoustic transducer, measures the groove depths of therespective grooves in real-time during polishing of the wafer. The depthmeasurement element 142 can be arranged on a scan arm (not shown) todiametrically scan over the polishing surface 112 during polishing tomeasure these groove depths. The surface condition analyzer 136 cancompare the respective measured groove depths to a predetermined groovedepth threshold, and the CMP controller 116 can notify a CMP operatorwhen the polishing pad 104 has reached the end of its useful life basedon the measured groove depths.

To determine a surface condition of conditioning disk 110, CMP system100 includes a torque measurement element 144 to measure a torqueexerted by the motor assembly 114 during polishing. A surface conditionanalyzer 136 then determines the condition of conditioning surface 126(and possibly the polishing surface 112 to some extent) based on themeasured torque. In making this determination, the surface conditionanalyzer 136 makes use of the fact that measured torque is proportionalto the amount of friction between the engagement and conditioningsurfaces 126, 112. Because the amount of friction measured is set by theconditioning surface's ability to “rough up” the polishing surface 112,the measured torque corresponds generally to the overall condition ofthe conditioning surface 126. For example, assuming equal slurrycompositions, temperatures, angular velocities, etc.; more measuredtorque generally corresponds to more friction between the conditioningsurface 126 and polishing surface 112, which generally corresponds to aless worn (e.g., newer) conditioning surface 126. Conversely, a lowertorque generally corresponds to smoother (e.g., older) conditioningsurface 126.

Based on the measured condition of conditioning surface 126, the CMPcontroller 116 can make real-time changes to CMP process parametersduring polishing in some embodiments. For example, as the conditioningsurface 126 becomes more worn (as indicated by less friction and lessmeasured torque), the CMP controller 116 can apply more down-force tothe conditioning disk 110 (and/or more up-force from the platen 102) sothere is greater frictional engagement between the conditioning surface126 and polishing surface 112. The CMP controller 116 can also applymore down-force to the wafer via the wafer carrier 108, can increase theplaten's angular velocity 122, can increase the wafer's angular velocity132, can alter the composition of slurry 111, and/or can increase thetemperature of the slurry 111 to increase the polish rate to offset thechange in conditioning surface 126. Other changes to CMP processparameters 140 could also be made.

In addition, in some embodiments, the surface condition analyzer 136 cancompare the measured torque to some predetermined torque threshold for agiven set of CMP process parameters 140, wherein the predeterminedtorque threshold corresponds to a torque at which the conditioning disk110 is to deemed “spent”. For example, for a given slurry composition,temperature, angular velocities, etc.; if the torque falls below somepredetermined torque threshold (indicating conditioning surface 126 istoo worn), the conditioning disk 110 is deemed spent. Thus, the CMPcontroller 116 can notify a CMP operator that it is time to replace theconditioning disk 110.

FIGS. 2-3 illustrate a more detailed view of one example of how groovedepths can be measured for a polishing pad 200. FIG. 2's polishing pad200 includes a number of grooves 202 a, 202 b, which have lower surfaces204 a, 204 b that are recessed relative to polishing surface 206.Although only two grooves are shown, it will be appreciated that anynumber of grooves ranging from one to hundreds or thousands of groovescan be included on the polishing pad 200, depending on the relativesizes of polishing pad and respective groove widths. A depth measurementelement 208, such as an acoustic transducer, measures groove depths ofthe respective grooves in real-time during wafer polishing. The depthmeasurement element 208 can be arranged on a scan arm (not shown) todiametrically scan over the polishing pad 200 during polishing—as shownby arrow 210.

In embodiments where depth measurement element 208 is an acoustictransducer, the acoustic transducer transmits an acoustic pulse or wave214 and subsequently measures a reflected acoustic pulse or wave 216which is based on the transmitted acoustic pulse or wave. Often, thismeasurement is carried out while a liquid 212, such as deionized wateror slurry for example, is present on the polishing pad 200 to help limitattenuation of the propagating acoustic pulse or wave. To measured thegroove depth, the acoustic transducer can analyze a time betweentransmission of the pulse or wave 214 and reception of the reflectedpulse or wave 216; or can measure a phase difference between thetransmitted pulse or wave 214 and received pulse or wave 216. Thus, tomeasure a first polishing pad thickness t1, the acoustic transducer willmeasure a first distance dl based on the time or phase differencebetween the transmitted and reflected waves or pulses. As the acoustictransducer continues its scan, it will see a change in the time or phasedifference as it starts to pass over groove. In particular, it will seea longer time delay between transmitted and reflected pulses or waves ora corresponding change in phase difference, which is indicative of asecond distance d1. By taking the difference between d1 and d2, theacoustic transducer can determine the corresponding groove depth.

If a measured groove depth is less than some predetermined groove depth,it can indicate the polishing pad is spent. Hence, in such an instance,a CMP controller can notify a CMP operator so the CMP operator canreplace the polishing pad 200 with a new polishing pad. Further, in someembodiments it is possible that the polishing ability of the polishingpad 200 changes as the pad wears. Because of this, monitoring the groovedepth in real-time allows the CMP system to account for changes in thepolishing characteristics of the polishing pad 200 as it wears. Forexample, as the polishing surface becomes more worn (as indicated bydiminished groove depths), the CMP controller 116 can apply moredown-force to the wafer via the wafer carrier 108, can increase theplaten's angular velocity 122, can increase the wafer's angular velocity132, can alter the composition of slurry 111, and/or can increase thetemperature of the slurry 111 to increase the polish rate or otherwisechange the CMP parameters to offset the change in polishing surface.

FIG. 4 show a cross-sectional side view of another CMP station 400 inaccordance with some embodiments. CMP station 400 comprises platen 402,polishing pad 404 supported by platen 402, wafer carrier 406 to holdwafer 408 proximate to polishing pad 404 during polishing, andconditioning disk 422 having conditioning surface 424. Wafer carrier 406includes an annular retaining ring 410, inside of which a pocket 412houses wafer 408. A plurality of concentric, variable-pressure elements(PE) 414 a-414 c are included on wafer carrier 406. The variablepressure elements 414, which are proximate to pocket 412, exertindependent amounts of suction or pressure onto corresponding concentricregions on the back-side of the wafer 408 a. Corresponding concentricsurfaces on the front of the wafer 408 b may be called “to-be-polished”wafer surfaces.

In some CMP processes, wafer 408 is held inside pocket 412 with upwardsuction applied to wafer's backside by variable pressure elements 414 soas to keep the wafer 408 raised above the lower face of retaining ring410. Platen 402 is then rotated about platen axis 418, whichcorrespondingly rotates polishing pad 404. Abrasive slurry 420 in thendispensed onto the polishing pad 404, and conditioning disk 422 islowered onto polishing pad 404. A platen motor (not shown) then beginsrotating wafer carrier 406 around platen axis 418. Meanwhile, wafercarrier 406 is lowered, retaining ring 410 is pressed onto polishing pad404, with wafer 408 recessed just long enough for wafer carrier 406 toreach polishing speed. When wafer carrier 406 reaches wafer polishingspeed, wafer 408 is lowered facedown inside pocket 412 to contact thesurface of polishing pad 404 and/or abrasive slurry 420, so that thewafer 408 is substantially flush with and constrained outwardly byretaining ring 410. Retaining ring 410 and wafer 408 continue to spinrelative to polishing pad 404, which is rotating along with platen 402.This dual rotation, in the presence of the downforce applied to wafer408 and the abrasive slurry 420, cause the wafer 408 to be graduallyplanarized. During this planarization process, the surface condition ofconditioning disk 422 and/or polishing pad 404 can be monitored inreal-time, and CMP parameters can be adjusted based on the measuredsurface condition(s).

After CMP, wafer carrier 406 and wafer 408 are lifted, and polishing pad404 is generally subjected to a high-pressure spray of deionized waterto remove slurry residue and other particulate matter from the pad 404.Other particulate matter may include wafer residue, CMP slurry, oxides,organic contaminants, mobile ions and metallic impurities. Wafer 408 isthen subjected to a post-CMP cleaning process.

FIG. 5 illustrates another method of planarization in accordance withsome embodiments of the present disclosure. While this method and othermethods disclosed herein may be illustrated and/or described as a seriesof acts or events, it will be appreciated that the illustrated orderingof such acts or events are not to be interpreted in a limiting sense.For example, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the disclosure herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

As FIG. 5 shows, method 500 starts at 502 when CMP process parametersare set for a CMP system. CMP process parameters can include, but arenot limited to: a polish time for which wafers are to be polished, adown-force to be applied to a to-be-polished wafer surface relative to apolishing pad, a down-force to be applied to the conditioning surface,an angular velocity of the polish pad or wafer, a slurry composition ora slurry temperature. A wafer typically includes a number of electricalconnections and electrical isolation regions that are established usingalternating layers of conductors and insulators.

In step 504, the method provides an abrasive slurry on a polishingsurface of the CMP system.

In 506, the method places a conditioning surface in frictionalengagement with the polishing surface to condition the polishingsurface. The conditioning surface typically has a hardness that isgreater than that of the polishing surface. For example, in manyembodiments the conditioning surface is a diamond encrusted surface.

In 508, the method places a to-be-polished wafer surface proximate tothe conditioned polishing surface.

In 510, the method polishes the to-be-polished wafer surface while usingthe CMP process parameters.

In 512, during polishing of the wafer, the method measures a surfacecondition of the polishing surface and/or conditioning surface.

In 514, the method adjusts one or more CMP process parameters duringpolishing based on the measured surface condition.

Thus, it will be appreciated that some embodiments relate to a CMPsystem. The CMP system includes a polishing pad having a polishingsurface, and a wafer carrier to retain a wafer proximate to thepolishing surface during polishing. A motor assembly rotates thepolishing pad about a polishing pad axis and concurrently rotates thewafer about a wafer axis during polishing of the wafer. A conditioningdisk has a conditioning surface that is in frictional engagement withthe polishing surface during polishing. A torque measurement elementmeasures a torque exerted by the motor assembly during polishing. Acondition surface analyzer determines a surface condition of theconditioning surface or the polishing surface based on the measuredtorque.

Other embodiments relate to a CMP system for polishing a wafer. This CMPsystem includes a platen arranged to rotate about a platen axis, and apolishing pad arranged over the platen. The polishing pad is arranged torotate about the platen axis coincidentally with the platen, andincludes a polishing surface having one or more grooves disposedtherein. A depth measurement element measures groove depths of therespective grooves in real-time during polishing of the wafer. Afeedback path adjusts a CMP process parameter in real-time based on therespective measured groove depths.

Another method relates to chemical mechanical polishing (CMP). In thismethod, a set of CMP process parameters are set. These CMP parametersare to be used to planarize one or more wafers. The method provides anabrasive slurry on a polishing surface of a CMP station. The methodplaces a conditioning surface in frictional engagement with thepolishing surface to condition the polishing surface. A to-be-polishedwafer surface is placed proximate to the conditioned polishing surface.The to-be-polished wafer surface is then polished while employing theset of CMP process parameters. During polishing of the wafer, the methodmeasures a surface condition of the polishing surface or conditioningsurface. A CMP process parameter can be adjusted during polishing basedon the measured surface condition.

Although the disclosure has been shown and described with respect to acertain aspect or various aspects, equivalent alterations andmodifications will occur to others skilled in the art upon the readingand understanding of this specification and the annexed drawings. Inparticular regard to the various functions performed by the abovedescribed components (assemblies, devices, circuits, etc.), the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (i.e.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary embodiments of the disclosure. In addition,while a particular feature of the disclosure may have been disclosedwith respect to only one of several aspects of the disclosure, suchfeature may be combined with one or more other features of the otheraspects as may be desired and advantageous for any given or particularapplication. Furthermore, to the extent that the terms “including”,“includes”, “having”, “has”, “with”, or variants thereof are used ineither the detailed description and the claims, such terms are intendedto be inclusive in a manner similar to the term “comprising”.

What is claimed is:
 1. A chemical mechanical polishing (CMP) system,comprising: a polishing pad having a polishing surface; a wafer carrierto retain a wafer proximate to the polishing surface during polishing; amotor assembly to rotate the polishing pad about a polishing pad axisand concurrently rotate the wafer about a wafer axis during polishing ofthe wafer; a conditioning disk having a conditioning surface, whereinthe conditioning surface is in frictional engagement with the polishingsurface during polishing; a torque measurement element to measure atorque exerted by the motor assembly during polishing; and a conditionsurface analyzer to determine a surface condition of the conditioningsurface or the polishing surface based on the measured torque.
 2. TheCMP system of claim 1, further comprising: a feedback path to adjust aCMP process parameter in real-time during polishing of the wafer basedon the surface condition determined by the condition surface analyzer.3. The CMP system of claim 1, wherein the polishing pad includes aplurality of grooves in the polishing surface, the CMP system furthercomprising: a depth measurement element to measure groove depths of therespective grooves during polishing of the wafer.
 4. The CMP system ofclaim 3, wherein the depth measurement element comprises an acoustictransducer to measure the groove depths while a liquid is present on thepolishing surface.
 5. The CMP system of claim 3, wherein the depthmeasurement element is arranged on a scan arm to diametrically traverseover the polishing pad to measure the groove depths of the respectivegrooves.
 6. The CMP system of claim 1, wherein the motor assemblyrotates the polishing pad about a platen axis at a first angularvelocity and rotates the wafer about a wafer carrier axis at an secondangular velocity.
 7. The CMP system of claim 6, further comprising: afeedback path to adjust the first angular velocity or the second angularvelocity based on the surface condition determined by the conditionsurface analyzer.
 8. The CMP system of claim 1, wherein the conditioningsurface has a hardness that is greater than a hardness of the polishingsurface.
 9. The CMP system of claim 8, wherein the conditioning surfaceis a diamond encrusted surface.
 10. The CMP system of claim 2, furthercomprising: a slurry dispenser to dispense an abrasive slurry onto thepolishing surface; wherein the feedback path is configured to adjust aslurry composition or slurry temperature based on the surface conditiondetermined by the condition surface analyzer.
 11. The CMP system ofclaim 2, wherein wafer carrier includes a plurality of concentric andvariable down-force elements adapted to apply respective down-forceswith respect to the polishing pad to concentric wafer regions; whereinthe feedback path is configured to adjust the respective down-forcesbased on the surface condition determined by the condition surfaceanalyzer.
 12. A chemical mechanical polishing (CMP) system for polishinga wafer, comprising: a platen arranged to rotate about a platen axis; apolishing pad arranged over the platen and arranged to rotate about theplaten axis coincidentally with the platen, the polishing pad includinga polishing surface having one or more grooves disposed therein; a depthmeasurement element to measure groove depths of respective grooves inreal-time during polishing of the wafer; and a feedback path to adjust aCMP parameter in real-time based on the respective measured groovedepths.
 13. The CMP system of claim 12, wherein the depth measurementelement comprises an acoustic transducer to measure the groove depthswhile a liquid is present on the polishing surface.
 14. The CMP systemof claim 13, wherein the liquid comprises slurry or deionized water. 15.The CMP system of claim 12, wherein the depth measurement element isarranged on a scan arm to diametrically traverse over the polishing padto measure the groove depths of the respective grooves.
 16. A method ofchemical mechanical polishing (CMP), comprising: setting a set of CMPprocess parameters to be used for planarizing one or more wafers;providing an abrasive slurry on a polishing surface of a CMP station;placing a conditioning surface in frictional engagement with thepolishing surface to condition the polishing surface; placing ato-be-polished wafer surface proximate to the conditioned polishingsurface; polishing the to-be-polished wafer surface while employing theset of CMP process parameters; and during polishing of the wafer,measuring a surface condition of the polishing surface or conditioningsurface.
 17. The method of claim 16, further comprising: adjusting a CMPprocess parameter during polishing based on the measured surfacecondition.
 18. The method of claim 16, wherein the surface condition ismeasured by measuring a torque of a motor assembly used to move thepolishing surface or wafer.
 19. The method of claim 16, whereinpolishing surface includes a number of grooves, and wherein the surfacecondition is measured by measuring depths of the respective groovesduring polishing.
 20. The method of claim 19, wherein the depths of therespective grooves are measured using an acoustic transducer.